You may do better checking out the mage forums for a question like this, but early simulations that Lhivera has posted indicate that all specs should ultimately be viable, with fire in the lead like it has been for every expansion. However, with all the balance knobs added as a result of the talent tree redesigns, it is quite possible that all specs will end up pretty close to one another.

In short: play what you like. Unless you end up in a hardcore, min/max guild, it shouldn't matter which spec you play.